The output power of, an electric machine is critically dependant on accurate synchronisation of phase excitation and rotor position. Accordingly, the electric machine typically includes a position sensor for determining the position of the rotor.
Following assembly of the electric machine, there is a tolerance in the alignment of the position sensor relative to the rotor. This tolerance in alignment results in a phase difference between the detected position and the actual position of the rotor. As a result, phase excitation and rotor position are not perfectly synchronised and thus the power and efficiency of the motor are compromised.
For many electric machines, tolerance in the alignment of the sensor is not regarded as a problem. This may be because the circumference of the rotor is relatively large and thus any tolerance in the alignment of the sensor results in a negligible phase difference between the detected and actual positions of the rotor. Alternatively, the output power and/or the efficiency of the electric machine are not critical and thus power losses that arise from sensor misalignment are deemed acceptable. However, for electric machines that are relatively small and/or where relatively high efficiency is required, tolerances in the alignment of the sensor present a significant problem.